This application for the Mentored Clinical Scientist Development Award is submitted so as to enable the candidate to gain necessary didactic and scientific training in developmental biology and molecular genetics, and to enable him to develop a career in academic reproductive endocrinology with a focus on molecular biology of oocyte and early embryo development as well as associated reproductive disorders. Elucidation of molecular mechanisms regulating gene expression during gametogenesis and early embryogenesis may have important implications for the understanding and treatment of reproductive problems such as oocyte aging, aneuploidy, and embryo loss. In this application, the candidate proposes to investigate a mammalian polyA binding protein (PABP) and its role in the regulation of gene expression during oocyte and early embryo development. Oocyte maturation is associated with suppression of transcription. Gene expression in mature oocyte and early embryo until the activation of zygotic transcription is regulated by translational activation and repression of maternally derived mRNAs. The first step in translational activation of stored maternal mRNAs is cytoplasmic extension of the polyA tail. A subsequent step is dissociation of the maskin-elF4E complex, so that the translationally essential elF4E-elF4G complex can form. Both of these processes have been intensively studied in the Xenopus oocyte. There, unmasking requires both cytoplasmic polyadenylation and a PABP. Although a cytoplasmic PABP (PABP1) has long been known, it is not expressed in oocytes and early embryos. The candidate has recently identified an oocyte and embryo-specific PABP in Xenopus named ePAB. As the predominant PABP during Xenopus early development and an inhibitor of deadenylation, ePAB most likely regulates polyA tail length and unmasking/translation of maternal mRNAs. Based on similarities between Xenopus and mouse in the molecular mechanisms regulating the control of cytoplasmic polyadenylation, the candidate hypothesized that a mammalian ePAB exists, and he identified a putative mouse ePAB ortholog. In this application, he aims to confirm the initial findings by determining its time- and tissue-specific expression pattern, and to further characterize its function in cytoplasmic polyadenylation, specifically in processivity and tail length control. Subsequently, the candidate will create an ePAB knock-out mouse. This application for the mentored grant K08 award is submitted so as to enable the candidate to gain necessary didactic and scientific training in developmental biology and molecular genetics, and to enable him to develop a career in academic Reproductive Endocrinology with a focus on molecular biology of oocyte and early embryo development and associated reproductive disorders.